1. Field of the Invention
The present invention relates to a probe testing method and apparatus for testing the shape of a leading end of a contact probe which is in pressure contact with a contact pad on an integrated circuit.
2. Description of the Related Art
At present, in the field of manufacturing circuit chips, each of which has an integrated circuit formed on a circuit substrate, a test is conducted for the integrated circuits in the manufactured circuit chips to see whether they are acceptable or defective. One of such tests involves bringing a leading end of a contact probe into pressure contact with the surface of a contact pad on an integrated circuit, and electrically determining from the contact probe whether the integrated circuit is acceptable or defective.
Generally, since an integrated circuit has a multiplicity of contact pads arranged in a predetermined pattern, a probe card having a multiplicity of contact probes arranged in correspondence to the contact pads is used for the aforementioned test. As such a probe card is brought into pressure contact with an integrated circuit, the multiplicity of probes are individually brought into pressure contact with the multiplicity of contact pads.
The contact probe as described above is made of a fine metal needle which has a leading end in such a shape that is optimal for conduction to a contact pad. Actually, however, the end shape of the contact probe can be inappropriate due to manufacturing variations, wear and the like, occasionally causing destruction of a contact pad if it is brought into pressure contact with such an inappropriate contact probe.
To prevent the destruction of contact pads, some probe testing apparatuses conduct a test after the end shape of contact probes has been manufactured or while the contact probes are in use. Such probe testing apparatuses are classified into a type which detects electric characteristics of contact probes, and a type which tests contact probes for their end shapes.
Methods of testing the end shape of a contact probe are further classified into a method of testing the end shape from the impression of a contact pad with which the contact probe is brought into pressure contact, and a method of directly testing the end shape of a contact probe. In the following, these testing methods will be outlined as representative prior art examples.
The first probe testing method for testing the end shape of a contact probe from the impression of a contact pad first scans the surface shape of the contact pad with which the contact probe is brought into pressure contact to read three-dimensional data of the surface shape.
For example, when the surface of the contact pad is parallel with the XY-directions, the three-dimensional data representing the surface shape has a multiplicity of X-direction main scanning lines arranged in the Y-direction, and represents irregularities in the Z-direction in its X-direction main scanning lines.
Next, for removing noise components from the read or scanned surface shape, the surface shape is partitioned into a dot matrix which extends in the XY-directions, and averages the depth of each dot in the Z-direction, for example, together with the depths of eight surrounding dots.
Then, from the averaged surface shape, recesses having a predetermined depth or more are extracted, and one having a predetermined area or more is selected from a plurality of extracted recesses. Since the impression of the contact probe is detected in this way, it is determined from at least one of the depth, position and shape of the impression whether the contact probe is acceptable or defective.
On the other hand, the second probe testing method for directly testing the end shape of a contact probe first images the end shape of the contact probe from an axial direction to read three-dimensional data of the end shape, and detects flat parts perpendicular to the axial direction from the imaged end shape.
This imaging relies on optical characteristics to detect only flat parts, and a level difference between the imaged flat parts is represented by interference fringes. Therefore, the level difference between the flat parts is calculated from the interference fringes to determine whether the contact probe is acceptable or defective depending on whether or not the level difference falls within a predetermined tolerance range.
Further, a third probe testing method for directly testing the end shape of a contact probe detects a flat part of the contact probe in a manner similar to the aforementioned approach, detects a maximum diameter and a minimum diameter from the detected flat part, and determines whether or not the contact probe is acceptable or defective depending on whether or not the ratio of the detected maximum diameter to minimum diameter falls within a predetermined tolerance range.
A fourth probe testing method for directly testing the end shape of a contact probe detects a flat part of the contact probe in a manner similar to the aforementioned approach, detects a maximum diameter and a perimeter from the detected flat part, and determines whether or not the contact probe is acceptable or defective depending on whether or not the ratio of the detected maximum diameter to perimeter falls within a predetermined tolerance range.
The first probe testing method described above relies on the surface shape of a contact pad to detect the impression of a contact probe from the depth and area of a recess, so that it can successfully detect the impression of the contact probe when the contact pad exhibits a high smoothness on the surface.
At present, however, over-wet-etching may be performed as appropriate to improve the contact property, in which case the etching advances in the direction of the grain boundary of aluminum which is the material for the contact pad, resulting in random miniature irregularities on the surface of the contact pad.
In addition, since the irregularities are similar to the impression of the contact probe in dimensions and shape, the first probe testing method fails to accurately detect the impression of a contact probe from the surface of an over-wet-etched contact pad.
The second probe testing method in turn relies on the level difference between flat parts to determine whether a contact probe is acceptable or defective, so that a defective contact probe will be determined as acceptable, for example, even if miniature bumps are found on the flat parts.
The third probe testing method in turn relies on the ratio of the maximum diameter to the minimum diameter of a flat part at the leading end of a contact probe to determine whether the contact probe is acceptable or defective, so that a defective contact probe even having an extremely distorted surface shape of the flat part will be determined as acceptable if there is a small difference between the maximum diameter and minimum diameter.
Finally, the fourth probe testing method relies on the ratio of the maximum diameter to the perimeter of a flat part at the leading end of a contact probe to determine whether the contact probe is acceptable or defective, so that even a good contact probe only having fine irregularities on the perimeter of the flat part, for example, will be determined as defective if the irregularities extend over a long distance to cause a long perimeter.